An analog-to-digital (AD) conversion circuit is widely used, and includes various kinds of conversion systems and for example, for high-speed use, a flash type AD conversion circuit is used and for the use in which the number of bits is large and latency may be slow, however, a speed to a certain level is desired, a pipeline type AD conversion circuit is used. However, in the case where the number of bits is large, the speed may be slow, a successive approximation routine (SAR) AD conversion circuit is used. The reference voltage used in AD conversion processing is generated in a digital-to-analog (DA) conversion circuit having a resistor string, a capacitive DA conversion circuit (CDAC) having a capacitor string and a switch string, or the like.
For the SAR type AD conversion circuit, an increase in speed is demanded and the AD conversion circuit the speed of which is increased by determining data corresponding to two bits at one step using three comparators has been proposed. However, at least three CDACs are used in order to generate the reference voltage to be supplied to the three comparators. In the case where a differential signal having a positive phase signal and a negative phase signal is AD-converted, six CDACs in total are provided.
It has also been proposed to generate the reference voltage described above to be supplied to the three comparators in a DA conversion circuit having a resistor string.